Rankine cycle apparatus have been known as systems for converting heat energy into mechanical work. The Rankine cycle apparatus include a structure for circulating water in the liquid and gaseous phases within a sealed piping system forming a circulation system in the apparatus. Generally, the Rankine cycle apparatus include a water supplying pump unit, an evaporator, an expander, a condenser, and pipes connecting between these components to provide circulation circuitry.
FIG. 18 hereof is a schematic block diagram of a general setup of a conventionally-known Rankine cycle apparatus (e.g., vehicle-mounted Rankine cycle apparatus) and certain details of a condenser employed in the Rankine cycle apparatus. The Rankine cycle apparatus of FIG. 18 includes a water supplying pump unit 110, an evaporator 111, an expander 107, and the condenser 100. These components 110, 111, 107 and 100 are connected via pipes 108 and 115, to provide circulation circuitry in the apparatus.
Water (liquid-phase working medium), which is supplied, a predetermined amount per minute, by the water supplying pump unit 110 via the pipe 115, is imparted with heat by the evaporator 111 to turn into water vapor (gaseous-phase working medium). The vapor is delivered through the next pipe 115 to the expander 107 that expands the water vapor. Mechanical device (not shown) is driven through the vapor expansion by the expander 107 so as to perform desired mechanical work.
Then, the expansion of the water vapor is terminated by lowering the temperature and pressure of the vapor and the resultant water vapor of the lowered temperature and pressure is delivered through the pipe 108 to the condenser 100, where the vapor is converted from the vapor phase back to the water phase. After that, the water is returned through the pipe 115 to the water supplying pump unit 110, from which the water is supplied again for repetition of the above actions. The evaporator 111 is constructed to receive heat from an exhaust pipe extending from the exhaust port of the engine of the vehicle.
The following paragraphs detail a structure and behavior of the condenser 100 in the conventional vehicle-mounted Rankine cycle apparatus shown in FIG. 18.
The condenser 100 includes a vapor introducing chamber 101, a water collecting chamber 102, and a multiplicity of cooling pipes 103 vertically interconnecting the two chambers 101 and 102. In the figure, only one of the cooling pipes 103 is shown in an exaggerative manner. Substantial upper half of the interior of each of the cooling pipes 103 is a vapor (gaseous-phase) portion 104, while a substantial lower half of the interior of the cooling pipe 103 is a water (liquid-phase) portion 105. In the vapor portion 104, most of the working medium introduced via the vapor introducing chamber 101 to the cooling pipe 103 is in the gaseous phase, while, in the water portion 105, most of the working medium flowing through the cooling pipe 103 is kept in the liquid (condensed water) phase. Boundary between the vapor 104 and the water 105 (i.e., gas-liquid interface) is a liquid level position 112.
One cooling fan 106 is disposed behind the cooling pipes 103 (to the right of the cooling pipes 103 in FIG. 18). The cooling fan 106 is surrounded by a cylindrical shroud 106a. Normally, operation of the cooling fan 106 is controlled by an electronic control unit on the basis of a water temperature at an outlet port of the condenser 100. The single cooling fan 106 sends air to the entire region, from top to bottom, of all of the cooling pipes 103 to simultaneously cool the cooling pipes 103.
The condenser 100 operates as follows during operation of the Rankine cycle apparatus. Water vapor of a relatively low temperature, discharged from the expander 107 with a reduced temperature and pressure, is sent into the vapor introducing chamber 101 of the condenser 100 via the low-pressure vapor pipe 108 and then directed into the cooling pipes 103. Cooling air 109 drawn into the cooling fan 106 is sent to the condenser 100.
Strong cooling air is applied by the cooling fan 106 to the upstream vapor portion 104 of the condenser 100, i.e. a portion of each of the cooling pipes 103 where a mixture of the vapor and water exists, and thus latent heat emitted when the vapor liquefies can be recovered effectively by the cooling air. Cooling air is also applied by the cooling fan 106 to the downstream water portion 105 of the condenser 100, i.e. a portion of each of the cooling pipes 103 where substantially only the water exists. Water condensed within the cooling pipes 103 of the condenser 100, is collected into the water collecting chamber 102 and then supplied by the water supplying pump unit 110 to the evaporator 111 in a pressurized condition as noted above.
In FIG. 18, reference numeral 116 represents a surface area of a condensing heat transmission portion, and 117 represents a surface area of a heat transmission portion of the condensed water. The surface areas 116 and 117 of the heat transmission portions and the liquid level position 112 have the following relationship.
The conventional Rankine cycle apparatus 100 inherently has the characteristic that the liquid fluid position 112 varies. Namely, because the engine output varies in response to traveling start/stop and transient traveling velocity variation of the vehicle, the amount of water supply to the evaporator 111 also varies, in response to which the liquid level position 112 within the condenser 100 varies. Namely, in the condenser 100, the liquid level position 112 rises when the amount of the vapor flowing into the condenser 100 (i.e., inflow amount of the vapor) is greater than the amount of the condensed water discharged from the condenser 100 (i.e., discharge amount of the condensed water), but lowers when the inflow amount of the vapor is smaller than the discharge amount of the condensed water. In this way, the vapor-occupied portion (104) in the cooling pipes 103 of the condenser 100 increases or decreases. Because the condensed water (in the portion 105) is discharged from the water supplying pump unit 110 subjected to predetermined flow rate control, a pressure from an outlet port 113 of the expander 107 to an inlet port 114 of the water supplying pump unit 110 is determined by a pressure within the condenser 100. The pressure within the condenser 100 is determined by an amount of condensing heat exchange caused by cooling of the vapor portion (104) of the condenser, and the amount of condensing heat exchange is determined by a flow rate of the medium to be cooled and a surface area of the condensing heat transmission portion 116. Thus, if the portion occupied with the vapor increases or decreases due to variation (rise or fall) of the liquid level position 112, the surface area 116 of the condensing heat transmission portion increases or decreases and so the pressure within the condenser 100 and the flow rate of the medium to be cooled do not uniformly correspond to each other any longer.
Similarly, the temperature of the condensed water at the outlet port of the condenser 100 is determined by an amount of heat exchange caused by cooling of the water portion (105) of the condenser, and the amount of the heat exchange of the condensed water is determined by the flow rate of the medium to be cooled and a surface area 117 of a heat transmission portion of the condensed water. Thus, if the portion occupied with the condensed water (105) increases or decreases due to variation (rise or fall) of the liquid level position 112, the surface area 117 of the heat transmission of the condensed water portion increases or decreases and so the temperature of the condensed water and the flow rate of the medium to be cooled do not uniformly correspond to each other any longer.
As noted above, the conventional condenser 100 is cooled in its entirety by means of the single cooling fan 106; that is, the gaseous-phase (vapor) portion 104 and the liquid-phase (water) portion 105 are cooled simultaneously by the same cooling fan 106. Therefore, although either one of the pressure within the condenser and the condensed water temperature can be controlled to agree with a target setting, both of the pressure within the condenser and the condensed water temperature can be controlled to agree with their respective target settings. Namely, if operation is performed by a human operator to control the pressure within the condenser through adjustment of the number of rotations of the cooling fan 106, the heat exchange amount in regions of the cooling pipes (condensed water cooling regions) where the water 105 exists also varies, so that the water 105 varies in temperature; thus, in this case, the condensed water temperature can not be controlled as desired. Conversely, if operation is performed to control the temperature of water (condensed water) 105 through adjustment of the number of rotations of the cooling fan 106, the heat exchange amount in regions of the cooling pipes (condensing regions) where the water vapor 104 exists also varies, so that the pressure within the condenser varies; thus, in this case, the pressure within the condenser can not be controlled as desired.
In the case where the condensed water temperature can not be controlled, and if the condensed water temperature increases, cavitations (bubbles) would be produced in the water supplying pump unit 110 located downstream of the condenser 100, which would result in deterioration in the pumping function of the pump unit 110. Conversely, if the condensed water temperature decreases, extra heat energy has to be consumed for subsequent re-heating of the water in the evaporator 111.
Also, in the case where the pressure within the condenser 100 can not be controlled as noted above, an increase in the pressure within the condenser 100 would lead to a decrease or decline in the output of the expander 107. Further, a decrease in the pressure within the condenser 100 would also produce cavitations (bubbles) in the downstream water supplying pump unit 110, which would result in deterioration in the pumping function of the pump unit 110.
Examples of the conventional condensers provided with a plurality of cooling fans are disclosed in Japanese Patent Laid-Open Publication Nos. 2002-115504 and SHO-63-201492.
Namely, the Rankine cycle apparatus disclosed in the 2002-115504 publication includes a separate cooling fan for each of the gaseous-phase and liquid-phase portions of the condenser so that the gaseous-phase and liquid-phase portions are cooled separately by the respective cooling fans. The 2002-115504 publication also discloses controlling the operation of the cooling fan for the liquid-phase portion on the basis of a detected temperature of water at an outlet port of the condenser.
Further, the SHO-63-201492 publication discloses a method for controlling a high-pressure condenser which includes two air blowers for cooling corresponding portions of the condenser. Depending on the situation, either or both of the air blowers are driven so as to control a total amount of cooling air supply to the condenser. Namely, the air-cooled high-pressure condenser includes the two air blowers and a condensed-water outlet adjusting valve, etc., and the pressure within the condenser is controlled with a pressure greater than the atmospheric pressure and the temperature of the condensed water is supercooled to 100° C. or below. Specifically, in the disclosed air-cooled high-pressure condenser, the pressure within the condenser is controlled through adjustment of the total amount of cooling air supply by changing the number of the air blower to be driven. Namely, the SHO-63-201492 publication never teaches providing two air blowers in corresponding relation to the gaseous-phase and liquid-phase portions and controlling the two air blowers independently of each other.
Further, a high-pressure condenser control device disclosed in Japanese Patent Laid-Open Publication No. HEI-10-185458 includes a first control that compares a difference between gaseous-phase and liquid-phase pressures within the condenser with a predetermined condenser water level setting and controls a condensed-water outlet adjusting valve so that the pressure difference becomes constant, and a second control that compares a gaseous-phase pressure within the condenser with a predetermined pressure setting and controls a single condenser cooling fan in such a manner that the gaseous-phase pressure becomes constant. Because only one condenser cooling fan is provided here, the disclosed control device presents a problem with the cooling arrangements as explained above in relation to FIG. 18.
Further, in the conventionally-known freezing machines, for example, there is also provided a condenser in a circulation system that circulates a working medium in liquid and gaseous phases. As illustrated in FIG. 19, the circulation system includes the condenser 301, expansion valve 302, heat exchanger (evaporator) 303 and compressor 304. In the conventionally-known freezing machines, the condenser 301, which communicates with the compressor 304 located upstream thereof, cools the gaseous-phase working medium supplied from the compressor 304 to thereby convert the gaseous-phase working medium into the liquid-phase working medium. Here, if a pressure increase occurs in the gaseous-phase portion of the condenser 301, the compressor 304 has to be driven in conformity with the pressure increase, which results in an increased workload. The extra workload can be avoided by performing optimal pressure control corresponding to a detected pressure within the condenser 301.
Also, the condenser 301 communicates at its downstream end with the expansion valve 302 located downstream thereof, and a supercooled liquid-phase working medium is supplied from the liquid-phase portion of the condenser 301 to the expansion valve 302. Variation in the intensity of the supercooling (i.e., variation in the temperature) would undesirably lower the cooling capability of the heat exchanger (evaporator) 303 communicating with the downstream end of the expansion valve 302. By performing temperature control corresponding to a detected temperature, it is possible to prevent the lowering of the cooling capability due to variation in the intensity of the optimized supercooling of the liquid-phase working medium and thereby secure a desired cooling capability. For the condenser 310 of the freezing machine too, independent optimal temperature control is required for each of the gaseous-phase and liquid-phase portions. For that purpose, it is desirable that the gaseous-phase and liquid-phase portions of the condenser 310 of the freezing machine be demarcated as separate objects of cooling control and cooled by respective sets of cooling elements (cooling fans, cooling water, etc.) while being controlled independently of each other. It is further desirable that physical objects to be controlled in the gaseous-phase and liquid-phase portions be set separately so that efficient cooling can be done in each of the gaseous-phase and liquid-phase portions.
Specifically, in the Rankine cycle apparatus, it is desirable that control be performed to retain an optimal pressure in the gaseous-phase portion of the condenser because the pressure in the gaseous-phase portion has great influences on various operations of the upstream expander and down-stream water supplying pump. If the pressure in the gaseous-phase portion is too high, the output of the expander would decline, while, if the pressure in the gaseous-phase portion is too low, cavitations would be produced in the water supplying pump. Thus, it is desirable to perform optimal control to avoid these inconveniences.
Also, control is performed to retain an optimal temperature in the liquid-phase portion of the condenser because the temperature in the liquid-phase portion has great influences on the behavior of the downstream water supplying pump. For example, if the temperature in the liquid-phase portion is too high, cavitations would be produced, and it is desirable to perform optimal control to avoid the inconvenience. Further, in the freezing machines, it is desirable that optimal pressure control corresponding to a detected pressure in the gaseous-phase portion of the condenser be performed on the gaseous-phase portion to avoid an extra workload and that optimal temperature control corresponding to a detected temperature in the liquid-phase portion of the condenser be performed in the liquid-phase portion to secure a desire cooling capability.
Namely, there has been a great demand for a novel technique which can cool the gaseous-phase and liquid-phase portions of the condenser independently of each other in accordance with respective criteria (pressure and temperature criteria) and efficiently on the basis of information indicative of the detected pressure within the condenser and detected temperature of the condensed water at the outlet port of the condenser in such a manner that the pressure within the condenser and temperature of the condensed water at the outlet port become optimal, and which can perform appropriate cooling control on the gaseous-phase and liquid-phase portions independently of each other.